Rake receiver and receiving method thereof

ABSTRACT

A disclosure of the present specification provides a rake receiver. The rake receiver may comprise: an oscillator; a radio frequency integrated circuit (RFIC) for processing analog signals, which are received after experiencing multipath propagation, according to a sampling clock generated by the oscillator and a carrier frequency clock; a rake processing unit for allocating fingers for each path to signals output from the RFIC, and then performing decoding, wherein the rake processing unit outputs information on a timing position through time tracking, a power metric sampled on-time, and the difference between a power metric at a half chip early-time and a power metric at a half chip late-time; and an auto frequency controller (AFC) for calculating a beta (β) value for adjusting the sampling clock of the oscillator according to the ratio of the difference between the power metric at the half chip early-time and the power metric at the half chip late-time to the power metric sampled on-time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2014/011461, filed on Nov. 27, 2014,the contents of which are hereby incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a terminal for a mobile communication.

Related Art

Mobile communication technologies has evolved through 2G and 3G into 4G.

FIG. 1 illustrates a mobile communication system.

As illustrated in FIG. 1, a mobile communication system includes atleast one base station (BS) 20. Each base station 20 provides a serviceto terminals 10 existing in specific geographic areas (which are, ingeneral, called cells) 20 a, 20 b, and 20 c.

The advancement of mobile communication technologies has enabled data tobe wirelessly transmitted and received at high speeds.

Further more, the terminals 100 goes beyond a regular phone whichprovides only a phone-call function, and has evolved into a smart phonewhich provides various functions, therefore improving User Experience(UE).

Meanwhile, many efforts have been being made recently to study andresearch a Machine Type communication (MTC) or an Internet of Things(IoT) which enables communication between devices and devices or betweena device and a server without human intervention. The MIC or the IoT isa concept of communication by a machine device, other than a terminalused by a human, over a wireless communication network. Such an MTC orIoT can be used in various fields, such as tracking, metering, payment,medical industries, and remote control techniques.

A device for the MTC or the IOT transmits a small amount of data, andsometimes needs to transmit and receive uplink/downlink data.

Considering the above characteristics, Wideband Code Division MultipleAccess (WCDMA), which is the 3G mobile communication, may be used forthe MTC or the IoT and reduce the costs of the device and battery powerconsumption.

One of the important characteristics of Code Division Multiple Access(CDMA), on which the WCDMA is based, is a rake reception function. Therake reception function is a function of separating two signalsaccording to time delay, the signals which are transmitted at the sametime from a base station but arrive a receiver at a different points intime (that is, with phase difference) due to multi-path fading. For thisreason, time synchronization is critical for the rake receptionfunction. If a timing offset occurs due to asynchronous time, it mayresult in degradation of performance.

Accordingly, a WCDMA receiver performs oversampling in order to reduce atiming offset. However, if a timing offset of ⅛ chip occurs whenfour-times oversampling is performed, it is not possible to compensatefor it. To reduce the timing offset of ⅛ to ½ chip, it may be possibleto increase the oversampling rate twice to perform 8-times oversampling,but it could also increase complexity considerably. In addition, evenwhen 8-times oversampling is performed, it is still not possible toovercome a timing offset of 1/16 chip.

In sum, increasing an oversampling rate results in an increase incomplexity and memory usage. Thus, it is not a perfect solution andfails to overcome a timing offset 1/(an oversampling rate*2).

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to solve theabove-mentioned problems.

To accomplish the aforementioned object, the present invention providesa configuration of a receiver which is capable of reducing a timingoffset without performing oversampling. In particular, the configurationof a receiver according to the present invention makes an oscillator tobe controlled based on information on a timing position, therebypreventing degradation of performance by the timing offset.

In an aspect, the present invention provides a rake receiver including:an oscillator; a radio frequency integrated circuit (RFIC) configured toprocess analog signals, which are received after experiencing multipathpropagation, according to a sampling clock and a carrier frequency clockof the oscillator; a rake processing unit configured to allocate afinger for each path of signals output from the RFIC, perform decoding,and output information on a timing position through time-tracking, apower metric sampled on time, and a difference between a power metric ata half chip early-time and a power metric at a half chip late-time; andan auto frequency controller (AFC) configured to calculate a beta (β)value for adjusting the sampling clock of the oscillator according to aratio of the difference between the power metric at the half chipearly-time and the power metric at the half chip late-time to the powermetric sampled on time.

In another aspect, the present invention provides a receiving method ofa rake receiver, comprising: processing analog signals, which arereceived after experiencing multipath propagation, according to asampling clock and a carrier frequency clock of an oscillator;outputting information on a timing position through time tracking basedon of the signals, a power metric sampled on time, and a differencebetween a power metric at a half chip early-time and a power metric at ahalf chip late-time; calculating a beta (β) value based on a ratio ofthe difference of the power metric at a half-time early time and thepower metric at a half-time late time to the power metric sampled at ontime; and adjusting the sampling clock of the oscillator based on thebeta (β) value.

According to the present invention, it is possible to reduce a timingoffset without performing oversampling, thereby reducing complexityfurther than a case where oversampling is performed. In particular,according to the present invention, by controlling an oscillator basedon information on a timing location, it is possible to preventdegradation of performance by the timing offset.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a mobile communication system.

FIG. 2 is a diagram illustrating the configuration of a general RadioFrequency (RF) unit.

FIG. 3 is a diagram illustrating the configuration of an RF unitaccording to an embodiment of the present invention.

FIG. 4 is a diagram illustrating detailed configuration of a rakeprocessing unit shown in FIG. 3.

FIG. 5 is example of an output of a filter shown in FIG. 4.

FIG. 6 is a block diagram illustrating a wireless communication systemin which an embodiment of the present invention is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentinvention. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the invention, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the present invention includesthe meaning of the plural number unless the meaning of the singularnumber is definitely different from that of the plural number in thecontext. In the following description, the term ‘include’ or ‘have’ mayrepresent the existence of a feature, a number, a step, an operation, acomponent, a part or the combination thereof described in the presentinvention, and may not exclude the existence or addition of anotherfeature, another number, another step, another operation, anothercomponent, another part or the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

As used herein, ‘wireless device’ may be stationary or mobile, and maybe denoted by other terms such as terminal, mobile terminal (MT), userequipment (UE), a mobile equipment (ME), mobile station (MS), userterminal (UT), subscriber station (ST), handheld device, access terminal(AT) and etc.

As used herein, ‘base station’ generally refers to a fixed station thatcommunicates with a wireless device and may be denoted by other termssuch as eNB (evolved-NodeB), BTS (base transceiver system), or accesspoint.

FIG. 2 is a diagram illustrating a configuration of a general RadioFrequency (RF) unit.

As illustrated in FIG. 2, a general rake receiver may include

a radio frequency integrated circuit (RFIC) 11, an oscillator 12, a rakeprocessing unit 13, and an auto frequency controller (AFC) 15.

The AFC 15 includes an accumulator 15-1, a phase-to-frequency converter15-2, an alpha (α) processing unit 15-7, an adder 15-8, and a delay unit(Z-1) 15-9. The AFC 15 measures difference between its frequency and afrequency of a transmitter, and controls the oscillator 12 so as toreduce the frequency difference.

Meanwhile, if a clock rate of the oscillator 12 is altered by the AFC15, it may affect a sampling clock so that it may result in a situationwhich is perceived as if even a timing position has been also moved. Theinventor of the present invention has paid attention on this situation.

As a result, the inventor of the present invention controls anoscillator with an offset value, which is capable of utilizing the abovesituation, to send a timing position in a direction where the maximumsignal-to-noise ratio (SNR) is obtainable.

That is, according to an embodiment of the present invention, in anattempt to overcome drawbacks of a general rake receiver and improveperformance, an oscillator is controlled to move a timing position to aposition where the maximum signal-to-noise ratio (SNR) is obtainable,thereby minimizing degradation of performance by a timing offset.

FIG. 3 is a diagram illustrating a configuration of an RF unit accordingto an embodiment of the present invention, and FIG. 4 is a diagramillustrating a detailed configuration of a rake processing unit shown inFIG. 3

As illustrated in FIG. 3, a rake receiver according to an embodiment ofthe present invention may include a radio frequency integrated circuit(RFIC) 131, an oscillator 132, a rake processing unit 133, an AFC 135.

The RFIC 131 receives analog signals which are received afterexperiencing multipath propagation. To this end, the RFIC 131 obtains asampling clock and a carrier frequency clock from the oscillator 132.

The rake processing unit 133 allocates a finger to each path of signalsreceived through the multiple path, and then performs decoding for eachsignal. The rake processing unit 133 estimates a phase metric throughthe operation of allocating fingers, and transmits the estimated phasemetric to the AFC 135. In addition, the rake processing unit 133 obtainsinformation on a timing position by performing time tracking.

The AFC 135 measures frequency difference with respect to thetransmitter, and controls the oscillator 132 to reduce the frequencydifference. the AFC 135 includes an accumulator 135-1, aphase-to-frequency converter 135-2, a beta (β) processing unit 135-4, analpha (α) processing unit 135-7, an adder 15-8, and a delay unit (Z-1)135-9.

The accumulator 135-1 accumulates a phase matric, transferred from therake processing unit 133, for a predetermined period of time. Thephase-to-frequency converter 135-2 calculates a frequency offset usingthe accumulated phase metric. To this end, the phase-to-frequencyconverter 135-2 may utilize an arc tangent function.

The beta (β) processing unit 135-4 acquires information on a timingposition from the rake processing unit 133, and obtains a beta (β) valuewhich matches the information on the timing position.

To determine the beta (β) value, it is necessary to acquire theinformation on a timing position from the rake processing unit 133, asdescribed above. To this end, the rake processing unit 133 may have animproved configuration as shown in FIG. 4.

As illustrated in FIG. 4, the rake processing unit 133 may include afinger unit 133-1, a plurality of down sampling units 133-2, a pluralityof descrambling and despreading unit 133-3, a plurality of matchingfilters 133-4.

The plurality of down sampling units 133-2 includes an on-time downsampling unit configured to perform sampling on time, a half chip earlydown sampling unit configured to perform sampling at a half chip earlytime, and a half chip late down sampling unit configured to performsampling at a half chip late time.

Thus, the rake processing unit 133 calculates a ratio according to thefollowing Equation 1.

$\begin{matrix}\frac{M_{{EL}\;\_\;{diff}}}{M_{Ontime}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In the above, Montime denotes a power matric sampled on time, andMontime denotes a difference between a power metric at a half chip earlytime and a power metric at a half chip late time with reference to apower metric of on time. Thus, Montime is MEL_diff=(Mearly−Mlate),wherein Mearly denotes a power metric at a half chip early time andMlate is power metric at a half chip late time.

That is, the rake processing unit 133 may calculate the information on atiming position based on a ratio of the difference between the powermetric at a half chip early time and the power metric at a half chiplate time to the power metric sampled on time, and then transfers theinformation on a timing position to the beta (β) processing unit 135-4.

The configuration of the rake processing unit 133 which is shown in FIG.4 is merely exemplary, and, if an additional timing tracker exists, theconfiguration of the rake processing unit 133 may not be the same as inFIG. 4.

Referring back to FIG. 3, when acquiring the information on a timingposition from the rake processing unit 133, the beta (β) processing unit135-4 obtains a beta (β) value which matches the information on a timingposition. The beta (β) processing unit 135-4 compensates for a frequencyoffset obtained from the phase-to-to frequency converter 135-2, byadding the beta (β) value to the frequency offset.

The alpha (α) processing unit 135-8 multiplies an alpha (α) value, whichis a scaling factor, for the frequency offset compensation. The adder135-8 adds up an output from the delay unit (Z−1) 135-9 and an outputfrom the alpha (α) processing unit 135-8, and outputs the result to theoscillator 132.

As such, the AFC controls the oscillator 132 to reduce a timing offsetso that degradation of performance by the timing offset may beminimized.

FIG. 5 is an example of an output of a filter shown in FIG. 4.

If the matching filter 133-3 shown in FIG. 4 utilizes a square rootraised cosine (SRRC) filter, the output power of the matching filter133-3 may be the same as shown in FIG. 5. In FIG. 5, the X-axisrepresents chip sections, and each section unit is 1/64 chip. A timingoffset value and a value of MEL_Diff/MOntime are mapped on a 1:1 basis,and the value of MEL_Diff/MOntime with respect to a specific timingoffset is shown in the following Table 1.

For example, if there is no interference and noise and a value ofMEL_Diff/MOntime is −0.2038, the current timing position is located upto 1/16 chip earlier than a position indicating the maximum SNR. Thus,if sampling is performed to reduce a sampling clock frequency, thetiming position may move backward.

Therefore, the beta (β) processing unit 135-4 may obtain a beta (β)value according to the following equation.

$\begin{matrix}{\beta = {x \times \frac{M_{{EL}\;\_\;{diff}}}{M_{Ontime}}}} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In the above equation, an value of x is a constant which is used todetermine a speed for movement to a timing position indicating themaximum SNR.

TABLE 1 Sample Offset SRRC Output Power 0 1  1/32 0.9967  2/32 0.9869 3/32 0.9707  4/32 0.9483  5/32 0.9202  6/32 0.8868  7/32 0.8486  8/320.8061  9/32 0.7601 10/32 0.7111 11/32 0.6600 12/32 0.6074 13/32 0.554114/32 0.5007 15/32 0.4479 16/32 0.3965 17/32 0.3468 18/32 0.2996 19/320.2552 20/32 0.2139 21/32 0.1762 22/32 0.1422 23/32 0.1120 24/32 0.085725/32 0.0633 26/32 0.0447 27/32 0.0297 28/32 0.0181 29/32 0.0097 30/320.0041 31/32 0.0010

TABLE 2 Ratio Between M_(EL)_Diff/M_(Ontime) Timing Offset 1/16 1/16 1/81/18 1/4 1/4 1/2 1/2 Chip Chip Chip Chip Chip Chip Chip Chip Early LateEarly Late Early Late Early Late Ratio −0.2038 0.2038 −0.4150 0.4150−0.8937 0.8937 −2.5221 2.5221

Meanwhile, to determine a value of x used in the above Equation 1, it isnecessary to consider the following.

Even though an actual frequency offset value is 0, a frequency offsetmay be measured as if the frequency offset exists. It is because autocorrelation properties of a scrambling code are different andinter-carrier interference (ICI) may affect a measurement of a frequencyoffset. In a case where an offset is located before a location of themaximum SNR, a positive (+) frequency offset or a negative (−) frequencyoffset may be measured according to a scrambling code. In the formercase, the AFC 135 performs a control operation to reduce a samplingclock frequency so that the offset may be moved to a timing positionindicating the maximum SNR. However, in the latter case, the offset ismoved to be far from the timing position indicating the maximum SNR.Thus, a value of x should be set to be greater than the maximum value,in which a frequency offset occurs, in a direction going far from atiming location indicating the maximum SNR. In this manner, it ispossible to move to a timing position indicating the maximum SNR withrespect to every scrambling code.

For example, in a case where a frequency offset is 0 in 3.84 Mcps WCDMAsystem, if a frequency offset of 20 Hz is measured in response tooccurrence of a timing offset of ⅛ chip according to autocorrelationproperties of a scrambling code,

${{{x \times \frac{M_{{EL}\;\_\;{diff}}}{M_{Ontime}}}} > 20},$

wherein a value of the constant x is greater than 48.2 because a valueof MEL_diff/MOntime is 0.4150 when an offset is ⅛ chip. That is, if avalue of the constant x is set to be greater than 48.2 in the aboveexample, a timing position is moved by the oscillator 132 to an on-timeposition.

The above-described embodiments of the present invention may beimplemented with various means. For example, the embodiments of thepresent invention may be implemented by hardware, firmware, software, ora combination thereof. Specific descriptions thereof is provided withreference to drawings.

FIG. 6 is a block diagram illustrating a wireless communication systemin which an embodiment of the present invention is implemented.

A base station 200 includes a processor 210, a memory 220, and an RFunit 230. The memory 220 is connected to the processor 210 to storevarious types of information necessary for driving the processor 210.The RF unit 230 is connected to the processor 210 to transmit and/orreceive a wireless signal. The processor 210 implements the suggestedfunctions, procedures, and/or methods. In the above-describedembodiments, operations of a base station may be implemented by theprocessor 210.

An wireless device 100 includes a processor 110, a memory 120, and an RFunit 130. The memory 120 is connected to the processor 110 to storevarious types of information necessary for driving the processor 110.The RF unit 130 is connected to the processor 110 to transmit and/orreceive a wireless signal. The processor 110 implements the suggestedfunctions, procedures, and/or methods. In the above-describedembodiments, operation of a wireless device may be implemented by theprocessor 110.

The processor may include an application-specific integrated circuit(ASIC), a different chip set, a logic circuit, and a data processingdevice. The memory may include a read-only memory (ROM), a random accessmemory (RAM), a flash memory, a memory card, a storage medium, and/orany other storage device. An RF unit may include a baseband circuit forprocessing a wireless signal. When the embodiment is implemented assoftware, the aforementioned scheme may be implemented as a module (aprocedure, a function, etc.) for performing the aforementionedfunctions. The module may be stored in the memory and implemented by theprocessor. The memory may be located inside or outside the processor, ormay be connected to the processor through a variety of means.

Regarding the above exemplary system, methods are described as a seriesof steps or blocks with reference to flow charts, but the presentinvention is not limited to the steps and a certain step may beimplemented at a different order or may be implemented simultaneouslywith other steps. In addition, it would be understood by those skilledin the art that the invention is not limited to the steps shown in theflowchart and that an additional step may be included or one or moresteps may be omitted therefrom without departing from the scope of thepresent invention.

What is claimed is:
 1. A rake receiver comprising: an oscillator; aradio frequency integrated circuit (RFIC) configured to process analogsignals, which are received after experiencing multipath propagation,according to a sampling clock and a carrier frequency clock of theoscillator; a rake processing unit configured to allocate a finger foreach path of signals output from the RFIC, perform decoding, and outputinformation on a timing position through time-tracking, a power metricsampled on time, and a difference between a power metric at a half chipearly-time and a power metric at a half chip late-time; and an autofrequency controller (AFC) configured to calculate a beta (β) value foradjusting the sampling clock of the oscillator according to a ratio ofthe difference between the power metric at the half chip early-time andthe power metric at the half chip late-time to the power metric sampledon time.
 2. The rake receiver of claim 1, wherein the beta (β) value iscalculated by${\beta = {x \times \frac{M_{{EL}\;\_\;{diff}}}{M_{Ontime}}}},$ whereinMontime is a power metric sampled on time, MEL_diff is the differencebetween the power metric at the half chip early-time and the powermetric at the half chip late-time, and x denotes is a constant foradjusting speeds.
 3. The rake receiver of claim 2, the beta (β) value isdetermined by a timing offset according to$\frac{M_{{EL}\;\_\;{diff}}}{M_{Ontime}},$ wherein the timing offset isdefined as in the following table M_(EL)_DiffM_(Ontime) ratio TimingOffset 1/16 1/16 1/8 1/18 1/4 1/4 1/2 1/2 Chip Chip Chip Chip Chip ChipChip Chip Early Late Early Late Early Late Early Late Ratio −0.20380.2038 −0.4150 0.4150 −0.8937 0.8937 −2.5221 2.5221.


4. The rake receiver of claim 2, wherein the beta (β) value foradjusting the sampling clock of the oscillator is determined so thatsampling is performed at an on-time position which is a time positionindicating a maximum signal-to-noise ratio (SNR).
 5. The rake receiverof claim 4, wherein the AFC sets the value of x to be greater when afrequency offset is measured to be negative (0) due to a timing offset,despite a real frequency offset of 0, because auto-correlationproperties are changed according to a scrambling code.
 6. A receivingmethod of a rake receiver, comprising: processing analog signals, whichare received after experiencing multipath propagation, according to asampling clock and a carrier frequency clock of an oscillator;outputting information on a timing position through time tracking basedon of the signals, a power metric sampled on time, and a differencebetween a power metric at a half chip early-time and a power metric at ahalf chip late-time; calculating a beta (β) value based on a ratio ofthe difference of the power metric at a half-time early time and thepower metric at a half-time late time to the power metric sampled at ontime; and adjusting the sampling clock of the oscillator based on thebeta (β) value.
 7. The receiving method of claim 6, wherein the beta (β)value is calculated by${\beta = {x \times \frac{M_{{EL}\;\_\;{diff}}}{M_{Ontime}}}},$ whereinMontime is the power metric sampled on time, MEL_diff is the differencebetween the power metric at the half chip early-time and the powermetric at the half chip late-time, and x is a constant for adjustingspeeds.
 8. The receiving method of claim 7, wherein the beta (β) valueis determined by a timing offset according to$\frac{M_{{EL}\;\_\;{diff}}}{M_{Ontime}},$ wherein the timing offset isdefined as in the following table: M_(ELDiff)/M_(Ontime) ratio TimingOffset 1/16 1/16 1/8 1/18 1/4 1/4 1/2 1/2 Chip Chip Chip Chip Chip ChipChip Chip Early Late Early Late Early Late Early Late Ratio −0.20380.2038 −0.4150 0.4150 −0.8937 0.8937 −2.5221 2.5221.


9. The receiving method of claim 7, wherein the beta (β) value foradjusting the sampling clock of the oscillator is determined so thatsampling is performed at an on-time position which is a timing positionindicating a maximum signal-to-noise ratio (SNR).
 10. The receivingmethod of claim 9, wherein a value of x is set to be greater when afrequency offset is measured to be negative (0) due to a timing offset,despite of a real frequency offset of 0, because autocorrelationproperties are changed according to a scrambling code.